Rabbit Achilles tendon full transection model - wound healing, adhesion formation and biomechanics at 3, 6 and 12 weeks post-surgery.

Gabriella Meier Bürgisser,Pietro Giovanoli,Elias Bachmann,Johanna Buschmann,Maurizio Calcagni,Gion Fessel,Jess G Snedeker

doi:10.1242/bio.020644

Abstract

ABSTRACTAfter tendon rupture repair, two main problems may occur: re-rupture and adhesion formation. Suitable non-murine animal models are needed to study the healing tendon in terms of biomechanical properties and extent of adhesion formation. In this study 24 New Zealand White rabbits received a full transection of the Achilles tendon 2 cm above the calcaneus, sutured with a 4-strand Becker suture. Post-surgical analysis was performed at 3, 6 and 12 weeks. In the 6-week group, animals received a cast either in a 180 deg stretched position during 6 weeks (adhesion provoking immobilization), or were re-casted with a 150 deg position after 3 weeks (adhesion inhibiting immobilization), while in the other groups (3 and 12 weeks) a 180 deg position cast was applied for 3 weeks. Adhesion extent was analyzed by histology and ultrasound. Histopathological scoring was performed according to a method by Stoll et al. (2011), and the main biomechanical properties were assessed. Histopathological scores increased as a function of time, but did not reach values of healthy tendons after 12 weeks (only around 15 out of 20 points). Adhesion provoking immobilization led to an adhesion extent of 82.7±9.7%, while adhesion inhibiting immobilization led to 31.9±9.8% after 6 weeks. Biomechanical properties increased over time, however, they did not reach full strength nor elastic modulus at 12 weeks post-operation. Furthermore, the rabbit Achilles tendon model can be modulated in terms of adhesion formation to the surrounding tissue. It clearly shows the different healing stages in terms of histopathology and offers a suitable model regarding biomechanics because it exhibits similar biomechanics as the human flexor tendons of the hand.

Highlights

IntroductionPlastic surgeons as well as trauma surgeons dealing with lacerated tendons are confronted with two main problems: re-rupture and
We developed two well-controlled adhesioninducing casting regimens where adhesion formation is shown to be modulated by the ankle angle used during immobilization
Adhesion provoking and adhesion inhibiting immobilization The adhesion extent was histologically assessed at 3 and 6 weeks post-surgery, where the legs of the rabbits had been immobilized with an angle of 180 deg in the 3-week group, while the 6-week group was divided into two subgroups subjected to different postoperative treatments (Fig. 1)

Summary

Introduction

Plastic surgeons as well as trauma surgeons dealing with lacerated tendons are confronted with two main problems: re-rupture and. In order to develop new suture techniques to enhance strength at the repair site (Buschmann et al, 2011; Haimovici et al, 2012) as well as biological (Crispim et al, 2015), cellular (Zhang et al, 2015), chemical (Zhao et al, 2013) or material-based (Sawadkar et al, 2014) strategies to overcome the formation of fibrous scar-like tissue and adhesion to the surrounding tissue, adequate non-murine animal models are needed to get insight into the impact of such approaches. A full transection tendon model with similar biomechanics as the human flexor tendons and a well-controlled adhesion induction would serve this need because full laceration injuries commonly are accompanied by scarry adhesions (Wu and Tang, 2013a,b)

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Discussion

Conclusion